Need some advice on power break booster pump noise

[tin-man]

Originally Posted by cobish

Maybe this will help


Now, the whine you hear when you rev your pump is one of three things. The first is the whine caused by pressure relief. It sounds kind of like a 'Shhhhhhhhh!' If you turn your wheel until it wont turn anymore, the fliud flow to the pump is cut off, and the pump is forced into pressure relief. On the F-car, this means a pressure of between 1200 and 1600 PSI. The pump has to recirculate this high pressure fluid within itself because the fluid has nowhere to go. If left in pressure relief for very long, the fluid can quickly exceed 325 degF, and break down, causing the pump to begin experiencing metal-to-metal contact.

The second noise is caused by cavitation. As you increase pump speed, more and more fluid is forced through the ports per unit time. There comes a velocity where the fluid just doesn't want to move that fast, and the vanes inside the pump will cause a vacuum, which is instantly filled with oil vapor. When the vane reaches the high pressure port, this vacuum cell is opened into a high pressure cell, and oil rushes to fill the void. A little 'sonic boom' results. These individual 'booms' are virtually microscopic, but they add up. What they translate into is a sound that sounds suspiciously like a whine. Now every pump cavitates. It's in the nature of moving fluid. By smoothing the radius of the ports, and relocating supercharge holes (I'm not going into that), engineers can reduce cavitation or push the frequency spectrum of the whine to a less noticable frequency. It is, in fact, where the bulk of pump engineering hours are spent.

Anyway, that funny high pitched whining that Mike Martin is hearing after his autocross run is the third type of noise. This type of whine is from the oil being aerated. When the pump is really screaming, the oil in the resivoir really gets churned up. This allows the occasional air bubble to pass into the pump, where it is totally pulverised into smaller bubbles. Eventually, the oil gets enough of these bubbles in it that you begin to hear it. If you want to really experience aeration, just run your pump low on oil!

None of these three types of noises will cause your pump to die. What kills a pump is heat and oil viscosity breakdown. The pressure relief example will overheat a pump in the extreme case causing galling of the bushing, or wear of the pump ring. The cavitation example, when extreme, like 7000-9000 RPM endurance runs, will cause microfractures to the pump internals and literally blow little flakes of metal off the walls. The extreme aeration example will cause increased heat to the internals, because air does not carry the heat away like oil does. But the common denominator to these is the word EXTREME. Most PS pumps never see this kind of duty, unless the person runs their pump low on oil. But none of us does this, because we all check our PS fluid as often as we check our trans fluid, right?

Thanks Cobish, I am guessing the same applies to power break booster pumps as well, thus what I am experiencing,based on this article,appears to be normal.

Cheers, John, AKA, tin-man